Temperature control device



Feb. 12, 1952 N. MILLER TEMPERATURE CONTROL DEVICE Filed April 6. 1949 Inventor Nicholas Miller Atfys .Patented Feb. 12, 1952 TEMPERATURE CONTROL DEVICE Nicholas Miller, Berwyn, Ill., assigner to Hotpoint Inc., a corporation oi' New York Application April 6, 1949, Serial N0. 85.89l

3 Claims.

The present invention relates to temperature control devices, and more particularly to thermal motors for operating such devices.

Although not limited thereto, the temperature control device of the present invention is especially useful in the automatic control of electric heating circuits employed in electric hot water heaters and the like, whereby the device responds to a temperature change in the tank of the hot water heater to open or to close electric contacts included in the electric heating circuits of the hot water heater in order to effect another desired temperature change in the tank. For example. the device may be employed to maintain `a substantially constant predetermined temperature of the tank of the electric hot water heater. v

A general object of the present invention is to provide an improved control device of the type noted that is simple, compact, rugged, readily assembled and relatively inexpensive to manufacture.

Another object of the invention is to provide in a control device of the type noted, an improved and exceedingly simple thermal motor for actuating a control member.

A further object of the invention is to provide a thermal motor of improved construction and arrangement in which the produced moyement is the characteristic equivalent to that of a long temperature responsive element, but in which the limited elastic yield is the characteristic equivalent to that of a short temperature responsive element.

Further features of the invention pertain to the particular arrangement of the elements of the temperature control device and of the thermal motor, whereby the above-outlined and additional operating features thereof are attained.

The invention, both as to its organization and method of operation, together with further obj ects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawing, in which Figure l is a longitudinal sectional view of a temperature control device embodying the prentinvention; Fig. 2 is a transverse sectional view of the temperature control device, taken in the direction of the arrows along the line 2-2 in Fig. 1; Fig. 3 is a plan view of the thermal motor incorporated in the temperature control device shown in Figs. 1 and 2; and Fig. 4 is a longitudinal sectional view of the thermal motor. taken in the direction of the arrows taken along the line 4 4 in Fig. 3.

Referring now to the drawing the temperature control device i I there illustrated, and embodying the features of the present invention, comprises a unitary thermal motor i2 including a relatively heavy rigid base I3 that is adapted to be secured in any suitable manner, not shown, to a hot water tank or other body, not shown, the temperature of which is to be controlled or regulated. In the event the base i3 is to be secured to the side wall of a substantially cylindrical body, the rear surface I3a thereof may be provided with a corresponding substantially cylindrical concavity, not shown, in order to insure a good ilt and good thermal contact therebetween so that there is no substantial temperature gradient between the body and the base I3 and so that the temperature of the base I3 closely follows the temperature of the body. The base i3 extends longitudinally and carries two rigid longitudinally spaced-apart abutments I4 and I5 projecting forwardly from the front face i312 thereof.

Also, the thermal motor I2 comprises a longitudinally extending rigid bar i6, a longitudinally extending exible and resilient element I1 and a rigid block I8 arranged in tandem relation between the abutments I4 and i5. More particularly, the bar ii is of substantially cylindrical configuration, and the lower end thereof is arranged in a recess Ha provided in the abutment I4 and pivotally mounted upon a laterally extending substantially cylindrical pin I9 rigidly secured in place in aligned openings provided in the abutment I4 on opposite sides of the recess Ila, the extreme lower end of the bar i8 having a substantially semicylindrical groove lia formed therein riding upon the outer cylindrical surface of the pin I. The block I8 is arranged in a recess lia formed in the abutment i5. The element i1 is of ribbon-like construction carrying knife edges lla and llb on the opposite ends thereof that are respectively received in cooperating laterally extending knife rests or grooves lib and I8b respectively formed in the extreme upper end of the bar I6 and in the lower face of the block i8. The element I1 is maintained under compression between the upper end of the bar IB and the lower face of the block Il so that it is forwardly offset or arched between the knife edges Ila and Hb with respect to the front face lib of the base i3. Further the central portion of the element i1 is provided with a threaded hole therein which receives the threaded shank of a forwardly projecting operating stud 20, the stud 20 being adjustable with respect to the element i1 and being locked in any adjusted position with respect to the element l1 by a lock nut 2| carried 3 on the shank thereof. The front face IIb of the base I3 is provided with a longitudinally extending dished-out recess I3c therein that receives the upper end of the bar II and carries two laterally spaced-apart and forwardly projecting guide posts 22 disposed on opposite sides of the recess I3c and cooperating with the opposite sides of the upper end of the bar I6. Preferably the base I3, the abutments I4 and I5 and the guide post 22 are formed of integral onepieee die east construction, whereby the base I3 is rigid between the abutments I4 and I5 and the guide posts 22 prevent lateral movement of the bar i6 while permitting longitudinal movement of the upper end thereof.

As illustrated in dotted lines in Fig. 4, after the pin I9 has been secured in place in the abutment Il and the block I8 has been placed in the recess Ia provided in the abutment I5, the bar IB and the element Il are assembled in tandem relation between the pin I9 and the block IB, and consequently between the abutments Il and I5. More particularly, the stud 20 is first secured in the opening provided in the mid-portion of the element Il and locked in place by the nut 2 I prior to assembly of the element I'I with the bar I6. The lower end of the bar I6 is then placed in the recess Ila provided in the abutment I4 with the groove IGa formed in the extreme lower end thereof riding upon the outer surface of the pin I9; and the knife edges Ila and I'Ib provided on the opposite ends of the element I1 are respectively positioned in the knife rest IGb formed in the extreme upper end of the bar I6 and in the knife rest Ib formed in the lower face of the block I8. The upper end of the bar I6 is then pressed inwardly toward the face I3b of the base I3, whereby the element I'I is buckled or arched between the knife edges IIa and IIb due to the resulting compression therein'. Further pivoting movement of the -bar I6 about the pin IS toward the front face I3b of the base I3 causes the upper end thereof to snap over center with respect to the pin I9, whereby the upper end of the bar IS enters into the recess I3c formed in the front face I3b and between the guide post 22, as illustrated in solid lines in Fig. 4. At this time the bar I6 occupies a stable position extending longitudinally upwardly toward the abutment I5 and inwardly toward the front face |327 of the base I3 and is securely retained in place in the recess I3c and between the guide post 22 due to the compression in the resilient element I1; and the element Il is held under initial compression to retain the initial offset or arch therein between the knife edges IIa and I'Ib and forwardly with respect to the front face I3b of the base I3. At this time a plane indicated at 23 passes through the knife rests IBb and I8b lies substantially parallel to the front face I3b of the base I3 and spaced forwardly with respect thereto; while a substantially parallel plane indicated at 24 passes through the center of the pin I9 is disposed slightly forwardly with respect to the plane 23, the offsetbetween the planes 23 and 24 being indicated by the distance S. This arrangement positively insures that the bar I6, the element I'I and the block I8 are restrained in stable assembled relation while permitting ready disassembly thereof, if required for purposes of inspection and adjustment, merely by following a procedure reversed from that described above.

Preferably the base I3 together with the abutments I4 and I5 and the guide posts 22 are formed of a stable aluminum alloy employing a die casting step; whereby the base I3 has a very high thermal coefficient of expansion. Preferably the pin I9, the bar I6, the element Il and the block I8 are formed of Invar, a nickel steel alloy comprising approximately 36 to 40 per cent nickel and 60 to 64 per cent iron, whereby these parts have a very low thermal coeilicient of expansion. In fact. for all practical purposes Invar has a thermal coeiiicient of expansion that is zero. Finally the operating stud 20 and the lock nut 2| may also be formed of Invar, although this is ordinarily not necessary as brass or bronze are entirely satisfactory. As illustrated in Fig. 4 when the parts of the thermal motor I2 are at an ambient temperature the effective over-all length oi the pin I3. the bar I6, the element II and the block Il in longitudinal tandem relation is indicated by the distance L; and the effective cord length of the arched element Il between the knife edges Ila and IIb is indicated by the distance C. Thus the base I3 over the distance L between the abutments I4 and I5 is formed of aluminum having a high thermal coemcient of expansion, while the parts I3, I6, II and Il over the distance L between the abutments Il and I5 are formed of "Invar having a thermal coefficient of expansion of substantially zero. Accordingly. it is immaterial whether the parts I3, II, I1 and Il are arrangedin good heat conducting relation with the base I3, since Invar" has a thermal coeilicient of expansion of substantially zero. and no consideration need be given to this aspect of the mounting arrangement of these parts with respect to the base I3.

Considering now the operation of the thermal motor I2 when the base I3 is at an ambient temperature the effective length of the base I3 between the abutments Il and I5 is equal to the distance L and the cord length of the arched element II is equal to the distance C, whereby a predetermined initial offset is established in the element I1 with respect to the front face IIb of the base I3. Accordingly, when the base I3 is at the ambient temperature the extreme front face of the stud 20 is spaced a predetermined initial distance with respect to the front face I3b of the base I3 depending upon the initial adjustment of the stud 2l and the cooperating lock nut 2| in the threaded opening provided in the midportion of the element I1. Assuming that the lock nut`2I has been rmly set, the initial distance between the extreme front face of the stud 20 and the front face I3b of the base I3 is established at the ambient temperature of the base I3. Now when the base I3 is heated due to contact with the hot body, not shown, the temperature thereof increases above the ambient temperature, whereby the base I3 having a very high thermal coefficient of expansion expands in all directions. Fundamentally and primarily the base I3 expands in the longitudinal direction, whereby the longitudinal distance between the abutments Il and I5 is substantially increased over the initial longitudinal distance L, relieving proportionately the compression exerted between the abutments' Il and I5 upon the pin I9, the bar Ii, the element I1 and the block I3 arranged in tandem relation therebetween. At this time the temperature of the parts I9, I6, Il and I8 is really not important as these parts have a thermal coeicient of expansion of substantially zero, although for convenience it may be assumed that the temperature of the parts mentioned fairly follows the temperature of the base I3. Since the parts I3, I8. I1 and I8 do not expand as the temperature thereof is increased, there is consequently a considerable reduction in the compression in these parts. Moreover, since the pin I3, the bar I6 and the block I8 are of rigid construction, this reduction in compression takes eiect primarily in the flexible element I1, whereby the cord distance between the knife edges I1a and I1b is considerably increased over the initial cord distance C. Accordingly, the amount of offset or arch in the element I1 is considerably reduced, whereby the extreme front face of the stud moves through a considerable distance toward the front face I3b of the base I3.

Conversely, when the base I3 is cooled as result of cooling of the hot body, not shown, the temperature thereof decreases toward the ambient temperature, whereby the base I3 contracts in all directions but fundamentally and primarily in the longitudinal direction decreasing the eil'ectlve longitudinal distance between the abutments Il and I5, whereby this longitudinal distance again approaches the initial longitudinal distance L, increasing proportionately the compression exerted upon the parts I9, IB, I1 and I8 disposed in tandem relation between the abutments I4 and I5. Since the parts I9, I6, I1 and I8 do not contract as the temperature thereof is decreased, there is consequently a considerable increase in the compression in these parts. Moreover, since the pin I9, the bar I6 and the block I8 are of rigid construction, this increase in compression takes effect primarily tance C a multiplication factor in the offset in the flexible element I1 between 1:4 and 1:10 may be readily obtained employing a construction of the general dimensions illustrated in the drawing. Hence, it will be understood that in response to a modest change in temperature in the hot body, not shown, the base I3 may expand over the distance L by approximately 0.001

inch producing a movement of the extreme front v face of the stud 20 toward the-front face I3b of the base I3 through a distance of as much as 0.010 inch. By increasing the length of one or both of the parts I6 and I8 the desired lateral movement of the stud 20 may be obtained while retaining the low elastic yield of the short arch. Thus it will be understood that the stud 20 may be utilized in order to actuate an electric switch or to control any other suitable device as explained more fully hereinafter.

in the flexible element I1, whereby the cord y distance between the knife edges I1a and I1b is considerably reduced toward the initial cord distance C. lAccordingly, the amount of offset or arch in the element I1 is considerably increased, whereby the extreme front face of the stud 20 moves through a considerable distance away from the front face I3b of the base I3.

0f course, the changes in compression in the parts I9, I6, I1 and I8 as a result of the change in temperature of the base I3 is actually dependent upon the differential in the deformation in the base I3 between the abutments I4 and I5 and the deformation in the parts I9, I6, I1 and I8. However, this differential is substantially equal in fact to the deformation in the base I3 as the parts I9, I6, I1 and I8 are really not eilectively expanded or contracted as a consequence of temperature changes over the entire response range of the thermal motor I2. Since the base I3 has a high thermal coefllcient of expansion the initial longitudinal distance L is materially changed in response to variations in temperature in the base I3; and since the parts I9, I6 and I8 are of rigid construction, this change in the initial longitudinal distance L takes place effectively and directly in the initial cord distance C. These changes in the initial cord distance C cause a multiplied movement in the offset or arch in the resilient element I1. Accordingly, the thermal motor I2 has a temperature response characteristic, with respect to the lateral deflection of the arch producing the movement of the stud ZI), which is equivalent to a long temperature responsive element of the length L, but obtaining this movement through the relatively short flexible member I1, which has the elastic yield characteristic equivalent to that of a short temperature responsive element of the length C. By transmitting these relatively great changes in the vlong distance L to the relatively short cord dis- I'he temperature control device I I in the present illustration further comprises electric switch structure carried by the base I3 of the thermal motor I2, which electric switch structure is preferably substantially identical to that disclosed in United States Patent No. 2,260,014, granted on October 2l, 1941, to Wallace J. Ettinger. More particularly, this switch structure comprises a substantially rectangular shaped casing 33 that is secured to the base I3 by a plurality of screws 3| extending through openings 32 provided in the base I3. The casing 30 may be made of any suitable insulating material, but is preferably made of a phenolic condensation product containing asbestos. Pivotally mounted within the casing 30 is a resilient operating member or arm 33, the operating member 33 extending longitudinally within the casing 30 and being disposed forwardly with respect to the parts carried by the base I3. Specifically, the upper end of the operating member 33 is attached to a pivot pin 34 carried by the casing 30; and the lower free end of the operating member 33 carries a short length of suitable bimetallic material or element 35 which serves as an ambient temperature compensating element in a well-known manner.

Provided in the operating member 33 adjacent to the fixed end thereof is a boss 35 that is engaged by the extreme front face of the stud 20 carried by the flexible element I1. The boss 35 and the stud 20 are arranged to be in engagement throughout the entire range of operation of the control device II. In order to effect the initial adjustment of the stud 20 so as to bring it into engagement with the boss 36 the shank of the stud 20 is threaded into the hole provided in the midportlon of the element I1 and is provided with a-.lock nut ZI as previously explained. Thus it will be understood that the movement of the stud 20 toward. and away from the front face I3b of the base I3 is transmitted directly to the boss 36 in order to cause a corresponding deflection of the operating member 33 about the pivot pin 34.

In order to control the deflection of the operating member 33 so that it will perform a desired switching operation and in order to provide for adjustment of the temperature at which the operating member 33 performs its switching function, an adjustable screw 31 is provided which is threadedly supported in a sleeve 38 mounted in an opening provided in the front of the casing 3D. The extreme rear end of the screw 31 is provided with a rounded portion 31' thatv is adapted to engage the operating member 33 at a point disposed intermediate the boss 36 anni the free end of the operating member 33. The screw 31 is provided on a shaft 39 which is adapted to extend forwardly outside of the casing 3B and to receive a suitable control knob 40. 'The control knob 4I) carries indicia 4I that cooperates with corresponding indicia provided on a front plate or cover 42 carried by the casing 30 in order to indicate the adjusted position of the temperature control device II. To effect a positive drive connection between the knob 43 and the shaft 39 there is provided a disk 43 that surrounds the shaft 39 and lies between the knob 4I) and a collar 44 formed integrally with the shaft 39. The drive connection between the disk 43 and the shaft 39 is obtained by a friction clamp formed by the disk 43, a plate 45 and a pair of screws 46, the parts mentioned being arranged tightly to grip the collar 44 therebetween. Provided on the disk 43 is a forwardly extending lug 41 inserted in the knob 43 to form the driving connection between the knob 43 and the disk 43. The plate 45 carries an outwardly projecting portion 45a that is adapted to engage a stud D carried by the casing 30 when the shaft 39 is rotated a predetermined amount in order to limit the movement of the screw 31 in either the clockwise or the counterclockwise directions. In order to prevent relative movement between the plate 45 and the disk 43 and to maintain a definite relation between these two parts, the plate 45 is slotted and a lug 48 carried by the disk 43 is inserted therein. Interposed between the plate 45 and the front wall of the casing is a flattened coil spring 43, this spring 49 serving to take up any play in the threaded connection between the screw 31 and the sleeve 38 and to maintain the knob 40 in its adjusted position.

Considering the operation of the above-described construction, it will be apparent that rotation of the knob 40 will cause the rear end 31 of the screw 31 to be moved either closer to or farther from the operating member 33. A ssuming that the screw 31 is rotated so that the rounded end 31 engages the adjacent portion of the operating member 33 and bears thereupon with a predetermined pressure, the expansion of the base i3 in accordance with an increase in temperature will cause the stud 25 to .move toward the front face I3b of the base I3, whereby the operating member 33 will first pivot about the rounded end 31 of the screw 31 as a fulcrum, effecting an opposite deflection of the free end of the operating member 33, the free end of the operating member 33 being moved toward the right away from the front face I3b of the base I3 as viewed in Fig. 1. This deflection in the free end of the operating member 33 is uti-lized to perform a switch controlling function as explained hereinafter. Continued movement of the stud 20 toward the front face I3b of the bast` I3 as a consequence of further expansion of the base I3 further relieves pressure upon the boss 3S, whereby the operating member 33 pivots further about the rounded end 31 of therscrew 3l.

t is thus apparent that the position of the rounded end 31 of the screw 31 relative to the operating member 33 determines the temperature at which the device II performs its switcl.- ing function.

As previously noted the device II is arranged to control the temperature of an electric hot water heater, or the like, and. accordingly, the operating member 33 controls switch structure comprising two pairs of front contacts 5I and 52 and one pair of rear contacts 53 with which an insulating bridging assembly 54 cooperates. More particularly, the bridging assembly 54 is operatively connected to the bimetallic element just above the lower free end thereof by an arrangement comprising a stud 55. The front of the bridging assembly 54 carries two bridging contacts 55 and 51 respectively cooperating with the pairs of contacts 5I and 52; and the rear of the bridging assembly 54 carries one bridging contact 53 cooperating with the pair of contacts 53. The pair of front contacts 5I are respectively mounted upon a pair of substantially L shaped brackets 5I respectively terminating in a pair of terminal screws 52 disposed adjacent to one side of the base I3, the pair of contacts 5I being positioned adjacent to the interior of the front wall of the casing 30 on the one side thereof. The pair of front contacts 52 are respectively mounted upon a pair of substantially L shaped brackets 53 respectively terminating in a pair of terminal screws 64 disposed adjacent to the other side of the base I3, the pair of contacts 52 being positioned adjacent to the interior of the front wall of the casing 30 on the other sidev thereof. The pair of rear contacts 53 are respectively mounted upon a pair of terminal studs 55 respectively extending through the side walls of the casing 30 and secured in place by associated locking nuts B5. The insulating bridging assembly 54 is of the fioating type to permit adjustment of the bridging contacts 55, 51 and 53 with respect to the associated pairs of contacts 5I, 52 and 53. Also, the rear contacts 53 are provided with threaded shanks engaging threaded openings pro- 3| vided in the terminal studs 65 so that the positions thereof may be readily adjusted with respect to the associated bridging contact 53, whereby the rear contacts 53 constitute limiting stops for the insulating bridging assembly 54. Finally, the shanks of the rear contacts 53 carry lock nuts 51 so that the adjusted positions thereof may be maintained. Thus the switching structure is of the double throw type, the front of the switching structure being double pole and the rear of the switching structure being single pole.

U shaped spring 1I. the spring 1I having a first arm bearing on a knife edge 35a provided on the extreme lower end of the bimetallic element 35 and having a second arm bearing on a fixed pivot 12. The pivot 12 comprises a stud that is 55 threaded in an opening formed in the lower end wall of the casing 30, the stud 12 being adjustable and being retained in its adjusted position by an associated lock nut 13. This adjustment is a factory adjustment and is provided for the purpose of initially setting the end thrust so that the switching structure opens and closes the associated circuits with a good snap action.

When the base I3 is at the ambient temperature the stud 20 engages the boss 35 forcing the operating member 33 forwardly with respect to the front face I3b of the base I3 as previously noted, whereby the portion of the operating member 33 engaging the rounded end 31 of the screw 31 fulcrums thereon causing the bimetallic element 35 to be moved into its position toward the front face I3b of the base I3 and consequently moving the spring 1I into its left-hand position as viewed in Fig. l. whereby the insulating bridging assembly 54 is moved toward the left as viewed in this figure. Thus at this time the bridging contact B establishes an electric circuit between the pair of rear contacts 53 and consequently between the terminal studs 65; and likewise the bridging contacts 56 and '51 respectively open the electric circuits between the pairs of front contacts 5I and 52 and consequently the respective electric circuits between the pairs of terminal screws 62 and 64.

Now when the temperature of the base I3 is increased the stud moving toward the front face I3b of the base I3 releases the pressure exerted upon the boss 36, whereby the operating member 33 is fulcrumed about the rounded end 31' of the screw 3l as previously explained. More particularly, the free end of the operating member 33 and the bimetallic element 35 move away from the front face I3b of the base I3 and upon predetermined movement thereof the spring 1I moves the contact insulating bridging assembly 54 from its left-hand position shown in Fig. 1 into its right-hand position with a snap action. When the insulating bridging assembly 54 is thus snapped into its right-hand position, the bridging contact 58 opens the electric circuit between the pair of rear contacts 53, and the bridging contacts 56 and 51 respectively close the electric circuits through the pairs of front contacts 5I and 52. It will be understood that the electric circuit through the pair of rear contacts l53 may be included in the principal heating circuit of the body, not shown, associated with the base I3; while the electric circuits through the respective pairs of front contacts 5I and 52 may comprise auxiliary heating or control circuits associated with the body, not shown. In any case it is contemplated that when the electric circuit through the pair of rear contacts 53 is closed that the temperature of the body, not shown, will be materially increased, and that when the electric circuit through the pair of rear contacts 53 is opened that the temperature of the body will be materially decreased. Accordingly, the temperature control device Il is effective to regulate the temperature of the body, not shown, with which the base I3 is operatively associated in accordance with the setting of the control knob 40. vThe base I3 may be directly secured in good heating exchange relation with the body, not shown, by any desired arrangement utilizing the holes 8| formed therein adjacent to the upper portion thereof. Also, in passing it is noted that two counter-bores 82 are formed in the lower portion of the base I3 in order to prevent engagement of the threaded shanks of the pair of rear contacts 53 with the base I3.

When the base I3 is secured to the body, not shown, the body, and, consequently, the control device I I, may be subjected to considerable variations in ambient temperature, and in order to prevent these variations in ambient temperature from producing fluctuations in the temperature at which the body, not shown, is governed by the control device I I,l the bimetallic element 35 is provided. The element 35 may be formed of two strips of metal having dissimilar thermal coeicients of expansion welded together, the strips being formed of different nickel-chrome steel alloys, or the like. The bimetallic element 35 is so arranged that when the ambient temperature increases causing the base I3 to expand, the bimetallic element 35 will curve toward the left, as viewed in Fig. 1, so as to counteract the movement of the free end of the operating member 33 toward the right, as viewed in this figure. Conversely, upon a decrease in ambient temperature 10 causing the base I3 to contract, the bimetallic element 35 will curve toward the right, as viewed in Fig. l, so as to counteract the movement of the free end of the operating member 33 toward the left, as viewed in this figure. Accordingly, the bimetallic element 35 compensates the control device Ii against iiuctuations in operation with reference to the setting of the control knob 40 resulting from variations in ambient temperature.

Finally, the control device II comprises a rear cover plate 9| closing the remainder of the rear of the casing 30 that is not closed by the base I3. Also, an opening I3d is formed through the base I3 in alignment with the threaded end of the operating stud 20 and the associated lock nut 2| permitting factory adjustment of the position of the stud 20 with respect to the flexible element II after the thermal motor I2 as a whole has been assembled with respect to the insulating casing 30.

In view of the foregoing it is apparent that there has been provided a temperature control device of improved construction and arrangement incorporating an improved and exceedingly simple thermal operating motor.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A thermal motor comprising a rigid base, two longitudinally spaced-apart rigid abutments carried by said base, one of said abutments having a laterally extending first notch formed therein, a laterally extending substantially cylindrical rigid pin arranged in said first notch, a longitudinally extending rigid bar having a laterally extending second notch formed in one end thereof and a first laterally extending knife-rest formed in the other end thereof, said second notch receiving and engaging said pin, a rigid block engaging the other of said abutments and having a second laterally extending knife-rest formed therein, a longitudinally extending iiexible element terminating at the opposite ends thereof in first and second laterally extending knife-edges, said iirst and second knife-rests respectively receiving and engaging said flrst and second knife-edges and mounting said element under compression in order to produce an oifset therein between said knife-edges, said base being formed of material having a high thermal coefficient of expansion and each of said pin and said bar and said block and said element beingformed of material having a substantially zero thermal coeiicient of expansion so that the differential between the deformation in said base between said abutments and the deformation in said pin and said bar and said block and said element between said abutments incident to a temperature change is effective to vary the compression in said element and consequently the offset therein between said knifeedges, and an operating member selectively governed in accordance with the offset in said element between said knife-edges.

2. The thermal motor set forth in claim 1, wherein said pin and said bar and said element and said block are normally retained in assembled relation between said two abutments by the compression in said element.

3. The thermal motor set forth in claim 1, wherein the junction between said iirst knife-rest and said first knife-edge is oiset toward said 11 base with respect to a line drawn between said rst notch formed in said one abutment and said second knife-rest formed in said block. and said other end of said bar is in engagement with said base so that said pin and said bar and said element and said block are normally retained in assembled relation between said two abutments by the compression in said element.

NICHOLAS MIILER.

REFERENCES CITED Number Number 12 UNITED STATES PATENTS Name Date Lippincott July 8, 1924 Mulvany Apr, 16. 1940 Fischer July 8, 1941 Ettinger Oct. 21, 1941 FOREIGN PATENTS Country Date France June 4, 1910 

